[Stoves] (no subject)

Sun Oct 27 14:28:18 CDT 2019

Dear Kevin

This is an interesting exploration that may yield consistent benefits is someone is using that rather dreadful device.

There are dozens of charcoal combustors in Africa and the one shown is one of the worst. Given that there are far better devices for burning charcoal, not to mention better ways to load the fuel, I am too surprised that just about anything you do would not improve it.

Cecil Cook and I assisted GTZ's ProBEC North in the period 2007-2010 to improve the appalling charcoal waste in Lusaka.  Cecil came up with an interesting analysis which was the result of interviewing users about how much money they could save before their pockets "grew holes". It was a bout 10 days income. Any stove that costs more than that was unlike to sell no matter what it did.

A second thing observed was the widespread used of a metal tube as a chimney to speed the ignition. It seems the second test was conducted without lighting the fuel properly. I wonder if the tube was used for these tests.

Two additional things that would make testing more convincing. First, there is far too much fuel in the stove. Do people really use a kg and light the whole thing to cook a meal? I would expect something between 500 and 700 g.

Second is that one should never have a pot sitting directly on the charcoal. It cannot possibly burn properly with the pot sitting on the fuel extinguishing the flames.

That stove usually has the pot sitting on top of the lip of the stove with the fuel burning under it. The pot seals to the stove and the gases exit through the holes. That is why (in part) it is such a terrible cooker. It has poor aeration and very high CO contributing to its performance.

More than ten years ago a much better stove was introduced, a metal version of the Maputo Ceramic Stove developed by a retired German metal worker from the MCS. This costs more than the one in the report, which I recall sells for about $1.50.

If that is the device someone is using, and the addition of the stones improves performance consistently, by all means continue. I'd like to see it operated with half the fuel loaded to represent more closely the typical pattern of use. I can't see the theoretical basis for the additional plate making any difference save that if it is loose, air can flow around the edge perhaps burning off some of the CO generated in the midst of the fire. As can be seen in the photo, elevating the fuel above the lip gets it into the open air where it can burn better.  It's is still pretty awful, though.

The Malgache stove popular in West and Central Africa is better from several points of view including that it elevates the pot above the fuel.

If you want to burn charcoal reasonably well there should be 50mm vertical space between the fuel and the pot. That region should be sheltered from cross winds and aeration should be provided that reaches almost to the centre, if possible.

As to the retention of heat in the stones, there is no doubt they will get hot. The main benefit of stored heat in a stove is to keep the char burning more completely as the fire dies.

How a bout trying the experiment again using 350 g of charcoal and break it up so it can burn at a rate high enough to provide the cooking power needed. The fuel particle surface to volume ratio defines this. If you want more power, get more surface area burning at the same time. It should fit into the space under the pot when it is sitting on the stove lip.

It is can cook with 200 g there would still be lots left.

Incidentally when burning a kg of charcoal and stopping with most of it left over, you should report the energy liberated as that of the charcoal ash-free (AF). This is because all the original ash in the fuel is still there at the end, which means the missing mass is combustible, not "average charcoal". Suppose the ash is 10%. Then the missing 200 g mass has the energy of 200/0.9 g = 222 g of charcoal with ash in it.

Regards
Crispin

From: info at sun24.solar
Sent: October 27, 2019 9:01 AM
To: stoves at lists.bioenergylists.org
Reply to: stoves at lists.bioenergylists.org
Subject: Re: [Stoves] (no subject)

Here is a report from Zambia<https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fdocs.google.com%2Fdocument%2Fd%2F167i50oweyfe23bRMnDSeJwlu0eM4IgTek6IO2C6JPes%2Fedit%3Fusp%3Dsharing&data=02%7C01%7C%7C5adb9b35eb164c863d8e08d75addc36c%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637077780832681885&sdata=YpL%2BDV4Jv3JJn7EOBjT5EA3jWIjF3B8CQkFz2NMriU0%3D&reserved=0> indicating that the rock bed and second metal grate improve the efficiency of the Zambian mbaula (all-metal) charcoal jiko by 41%.  Cooking time is also greatly reduced.  While these testers have no training, their results are consistent.

This is such a simple modification that dissemination could be very rapid.  I hope some of you can try this.

On Thu, Oct 10, 2019 at 1:37 PM K McLean <info at sun24.solar<mailto:info at sun24.solar>> wrote:
Listmates,

Has anyone tried this?

We seem to have significantly increased the efficiency of charcoal jikos by putting a bed of rocks on the jiko's grate and putting second metal grate on the rock bed.  The charcoal goes on the second metal grate.   2-3 cm rocks work.  It works in all metal jikos and clay jikos that we've tested.

Our testing is early and unscientific, but consistent.  25-50% less fuel used.  Here are three reports.  The Sierra Leone report has good photos at the bottom.

Sierra Leone<https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fdrive.google.com%2Ffile%2Fd%2F12MvBKjxq6PCGCcCHAjSYSeVXXvl7jWjD%2Fview%3Fusp%3Dsharing&data=02%7C01%7C%7C5adb9b35eb164c863d8e08d75addc36c%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637077780832691902&sdata=MqY7JaMTSg6tod8s%2BlvxR09foMAMqHWo2jqMdgCklfs%3D&reserved=0>

Uganda<https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fdrive.google.com%2Fopen%3Fid%3D1zQIY49E1vrfjYl7t5V_shvw70d67QirGWUrbW51tDxo&data=02%7C01%7C%7C5adb9b35eb164c863d8e08d75addc36c%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637077780832701907&sdata=agj%2F%2BbtHo6x%2FmUbUkLDYsXFkDWtBy89LwA7wrlnlBQo%3D&reserved=0>

Kenya (very few rocks)<https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fdrive.google.com%2Fopen%3Fid%3D1MPwHCwKEVqJvuybKB5Yj39nr8fbcopBP&data=02%7C01%7C%7C5adb9b35eb164c863d8e08d75addc36c%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637077780832711912&sdata=xQLz%2FJ6%2FdVVAD%2FkEfaX3r5phX01diAfAeimEmNph6Mo%3D&reserved=0>

(The report authors are untrained and not native English speakers.  Especially the Kenya report contains many errors. Please focus on the consistent final conclusion that a rock bed and second metal grate significantly reduce firewood usage.)

This may be a very low cost, very easy way to greatly improved the efficiency of charcoal jikos.  I'd like to hear if there is already a body of work on this.  Here is my rough drawing:

[20191010_133359.jpg]

Thank you,
Kevin

Kevin McLean, President
Sun24
https://sun24.solar<https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fsun24.solar&data=02%7C01%7C%7C5adb9b35eb164c863d8e08d75addc36c%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637077780832721923&sdata=Nsi14Kx03q4Xt4fYf%2FB9uW3JZpWTcQO2B13z5xUOBkM%3D&reserved=0>  Sun24 Cookstoves Overview<https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fdocs.google.com%2Fdocument%2Fd%2F1ZryS7gQ1q3zKLZPM2KcXdtIHbOYQp4PbloPqMvrlZ5Y%2Fedit%3Fusp%3Dsharing&data=02%7C01%7C%7C5adb9b35eb164c863d8e08d75addc36c%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637077780832731922&sdata=%2BqrwLKvoaPGUOXCbz78k4n%2BF7o5eqUqQVxZtyfVd7eE%3D&reserved=0>
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             [https://docs.google.com/uc?export=download&id=13teZQbnv_6ek6JkEy-4n0yyUVTrl3M2W&revid=0B8zNcWsuiuj3N2RuVFFYL3EvdElxR1lDcm9QQVlaL0F4VnVFPQ]         [https://docs.google.com/uc?export=download&id=11k6wcaMcCbykOoLu-Qo4n6Kbdhplk_er&revid=0B8zNcWsuiuj3ejdsRjRXQWU2OW4rVUpwMUx0Q0U0eXgxcStBPQ]

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